The present invention relates to batteries.
Batteries, such as alkaline batteries, are commonly used as energy sources. Generally, alkaline batteries have a cathode, an anode, a separator and an electrolytic solution. The cathode is typically formed of manganese dioxide, carbon particles and a binder. The anode can be formed of a gel including zinc particles. The separator is usually disposed between the cathode and the anode. The electrolytic solution, which is dispersed throughout the battery, can be a hydroxide solution.
The invention relates to batteries, such as alkaline batteries, having cathodes that include manganese dioxide and relatively small nonsynthetic, nonexpanded graphite particles. These batteries have good performance characteristics. For example, the batteries can exhibit high energy output at a high discharge rate, such as a discharge rate equal to at least the battery""s capacity (in units of Ampere-hours) discharged in one hour. The batteries can have various industry standard sizes, such as AA, AAA, AAAA, C or D.
xe2x80x9cNonsynthetic graphite particlesxe2x80x9d refer to graphite particles that are prepared without using an industrial or laboratory graphitization process.
xe2x80x9cNonexpanded graphite particlesxe2x80x9d refer to graphite particles that are prepared without any industrial or laboratory particle expansion process.
In one aspect, the invention features a cathode that includes manganese dioxide and nonsynthetic, nonexpanded graphite particles having an average particle size of less than about 20 microns.
The particle size is measured using a Sympatec HELIOS analyzer. For a given sample of graphite particles, the average particle size is the particle size for which half the volume of the sample has a smaller particle size.
In another aspect, the invention features an electrochemical cell including a cathode, an anode and a separator disposed between the cathode and the anode. The cathode includes manganese dioxide and nonsynthetic, nonexpanded graphite particles having an average particle size of less than about 20 microns.
In some embodiments, the separator includes a nonwoven, non-membrane material and a second nonwoven, non-membrane material disposed along a surface of the first material. In these embodiments, the separator can be devoid of a membrane layer or an adhesive layer disposed between the nonwoven, non-membrane materials. A membrane material refers to a material having an average pore size of less than about 0.5 micron, whereas a non-membrane material refers to a material having an average pore size of at least about 5 microns.
The cathode can have a porosity of from about 21% to about 28%. The porosity of the cathode is the relative volume of the cathode that is not taken up by solid material, such as, for example, manganese dioxide, graphite particles and binder.
The anode can have a porosity of from about 2 grams of zinc particles to about 2.45 grams of zinc particles per cubic centimeter of anode volume that is taken up by liquid or solid material.
The battery can have a relatively small amount of manganese dioxide and/or zinc particles compared to the amount of electrolytic solution. For example, the weight ratio of manganese dioxide to electrolytic solution can be from about 2.2 to about 2.9, and the weight ratio of zinc particles to electrolytic solution can be from about 0.9 to about 1.25. This is calculated based on the amount of electrolytic solution dispersed throughout the cathode, the anode and the separator.
The batteries can be AA or AAA batteries that demonstrate good results when tested according to the cc photo test, the 1 Watt continuous test, the half Watt continuous test, the pulsed test, the half Watt rm test and/or the quarter Watt rm test. These tests are described below.
Other features and advantages of the invention will be apparent from the description of the preferred embodiments thereof and the claims.